From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A48E8C7112A for ; Sun, 14 Oct 2018 15:33:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7739720890 for ; Sun, 14 Oct 2018 15:33:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7739720890 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728489AbeJNXPE (ORCPT ); Sun, 14 Oct 2018 19:15:04 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36300 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728180AbeJNXME (ORCPT ); Sun, 14 Oct 2018 19:12:04 -0400 Received: from [2a02:8011:400e:2:cbab:f00:c93f:614] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1gBiLr-0004cW-FC; Sun, 14 Oct 2018 16:30:43 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gBiLX-0000Ve-8S; Sun, 14 Oct 2018 16:30:23 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Dave Chinner" , "Tetsuo Handa" , "Tejun Heo" , "Jens Axboe" , "Jan Kara" , "syzbot" Date: Sun, 14 Oct 2018 16:25:41 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 258/366] bdi: Fix oops in wb_workfn() In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:cbab:f00:c93f:614 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Jan Kara commit b8b784958eccbf8f51ebeee65282ca3fd59ea391 upstream. Syzbot has reported that it can hit a NULL pointer dereference in wb_workfn() due to wb->bdi->dev being NULL. This indicates that wb_workfn() was called for an already unregistered bdi which should not happen as wb_shutdown() called from bdi_unregister() should make sure all pending writeback works are completed before bdi is unregistered. Except that wb_workfn() itself can requeue the work with: mod_delayed_work(bdi_wq, &wb->dwork, 0); and if this happens while wb_shutdown() is waiting in: flush_delayed_work(&wb->dwork); the dwork can get executed after wb_shutdown() has finished and bdi_unregister() has cleared wb->bdi->dev. Make wb_workfn() use wakeup_wb() for requeueing the work which takes all the necessary precautions against racing with bdi unregistration. CC: Tetsuo Handa CC: Tejun Heo Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 Reported-by: syzbot Reviewed-by: Dave Chinner Signed-off-by: Jan Kara Signed-off-by: Jens Axboe [bwh: Backported to 3.16: - Use bdi_wakeup_thread() instead of wb_wakeup() - Adjust context] Signed-off-by: Ben Hutchings --- fs/fs-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1071,7 +1071,7 @@ void bdi_writeback_workfn(struct work_st } if (!list_empty(&bdi->work_list)) - mod_delayed_work(bdi_wq, &wb->dwork, 0); + bdi_wakeup_thread(bdi); else if (wb_has_dirty_io(wb) && dirty_writeback_interval) bdi_wakeup_thread_delayed(bdi);